Powder coatings from mixtures of thermoplastic vinylidene fluoride based resins and polyamide resins

ABSTRACT

Pigmented and unpigmented polymeric resin blends containing up to 45 weight percent polyvinylidene fluoride based polymer and either polyamide 11 or polyamide 12 having particular usefulness in powder coating of objects are disclosed.

This application claims priority from U.S. Provisional Application Ser.No. 60/055,605, filed Aug. 12, 1997.

FIELD OF THE INVENTION

This invention relates to compositions of matter classified in the artof chemistry as polymers based on fluoropolymers, more specificallyhomopolymers of vinylidene fluoride (VDF) and copolymers of vinylidenefluoride with comonomers selected from hexafluoropropylene (HFP)tetrafluorethylene (TFE), chlorotrifluorethylene (CTFE),trifluoroethylene (TrFE), and/or vinylfluoride (VF), in combination withpolymers, more specifically non-thermosetting polyamide (nylon)polymers, to compositions containing them, more specifically to powdercoating compositions containing them, and to processes for thepreparation and use of the compositions containing the fluoropolymersand polyamide polymers and for the use of the fluoropolymer andpolyamide polymer combinations themselves.

BACKGROUND OF THE INVENTION

U.S. Pat. No. 5,106,910 describes a mixture of polyvinylidene fluoride,nylon 11 and a compatible adhesive to secure the coating to thesubstrate. The preferred composition is polyvinylidene fluoride, nylonand a nylon terpolymer/caprolactam adhesive. The coating is preferablyapplied by plasma spray.

U.S. Pat. No. 3,340,222 suggests inter alia that amide group containingpolymers may be used in connection with fluoropolymers to aid in filmformation and ultimate coating performance. At a maximum 50% of thecombination is to be the amide group containing polymer and on closerexamination of the text it its clear that the amide containing polymersreferred to are acrylamide polymers not polyamide polymers.

U.S. Pat. No. 3,826,794 describes the addition of selected polyamidepolymers to polyvinylidene fluoride based polymers for the purpose ofimproving the impact strength of PVDF polymers. The amount of polyamideis from 30% to 55% by weight and the choice of polyamide is stated to becritical. Polyamide from aminoundecanoic acid, polyamide (nylon) 11 ifmade from the commonly available aminoundecanoic acid,10-aminoundecanoic acid, is specifically stated to be incompatible withPVDF polymers along with polyamides from 6-aminocaproic acid.

Suitable polyamides are stated to be those described from brancheddiamines having carbon chain lengths defined in the patent.

The present invention provides mixtures of PVDF polymers and polyamide11, or polyamide 12, having less than 45%. by weight PVDF polymers whichare fusible powders suitable for providing pigmented or unpigmentedcoatings on substrates, particularly metal substrates and which are alsocapable of being formed by common techniques, such as by injectionmolding or extrusion, into two or three dimensional objects havingsuperior surface properties to corresponding polyamides not containingthe PVDF polymers. The compositions of the instant inventions are freeof the compatible adhesive of U.S. 5,106,910.

SUMMARY OF THE INVENTION

The invention provides in a first composition aspect a resin compositionconsisting essentially of a blend of from 0.01% up to 45% by weightpolyvinylidene fluoride based polymer and from greater than 55% to99.99% by weight polyamide polymer selected from the group consisting ofpolyamide 11 and polyamide 12.

The tangible embodiments of the first composition aspect of theinvention possess the inherent applied use characteristic of beingfusible to provide coatings on substrates having high stain resistance,good weatherability and flexibility, good scuff, wear and abrasionresistance while having good adhesion to the substrate on which they arecoated with good gloss and overall appearance.

The invention provides in a second composition aspect, an article ofmanufacture comprising a substrate coated on at least one surfacethereof with a coating formed from the first composition aspect of theinvention.

The invention provides in a third composition aspect, an article ofmanufacture comprising a three-dimensional object formed by applying alow shear forming method to a composition as defined in the firstcomposition aspect of the invention.

DEFINITIONS

"Polyamide 11" means poly 11-aminoundecanoic acid.

"Polyamide 12" means poly 12-amino lauric acid.

"Polyvinylidene fluoride based polymer," "PVDF polymer" or "PVDF resin"means polyvinylidene fluoride or copolymers of vinylidene fluoride withcomonomers such as hexafluoropropylene, tetrafluoroethylene,chlorotrifluoroethylene, trifluoroethylene, and/or vinylfluoride. Theinclusion of small quantities of terpolymers of vinylidene fluorideamong the copolymers is contemplated by the invention.

The inclusion of the vinylidene fluoride, tetrafluoroethylene,hexafluoropropylene terpolymer of U.S. Pat. No. 5,346,727 in quantitiesup to about 5% by weight in the dry resin PVDF polymer mixture iscontemplated as is inclusion of the terpolymers of European PatentApplication 0659846A2. The terpolymers may be blended into the startinglatex before isolation of the PVDF polymer resin or they may be blendedin later in the dry state.

"Consisting essentially of" in this specification and the appendedclaims means the compositions described and claimed are substantiallyfree of the compatible adhesive as described in U.S. Pat. No. 5,106,910,but they may contain the other permissible additives described asoptions in this specification.

DETAILED DESCRIPTION OF THE INVENTION

The invention will now generally be described with reference topreferred embodiments thereof so as to enable one of skill in the art tomake and use the same.

The vinylidene fluoride homo- and co-polymer resins employed as startingmaterials are known, as are their methods of preparation. See, forexample Humphrey and Dohany, Vinylidene Fluoride Polymers, Encyclopediaof Polymer Science and Engineering, 2nd Edition, Vol. 17, pp 532 to 5481989, John Wiley and Sons, and the references cited therein. See alsoU.S. Pat. Nos. 3,857,827; 4,360,652; 4,569,978; 3,051,677; 3,178,399;5,093,427; 4,076,929; 5,543,217; Moggi et al., Polymer Bulletin, 7, pp115 to 122, (1982), Bonadardelli et al., Polymer, 27, pp. 905-909(1986), Pianca, et al., Polymer, 28, pp 224 to 230 (1987), and Abuslemeet al., European Patent Application No. 650,982, A1. The resins soprepared may be homopolymer PVDF or copolymer PVDF with suitablemonomers for copolymerization with VDF being selected from HFP, CTFE,TFE, TrFE, VF or mixtures thereof. HFP is a preferred comonomer.

Up to about 30% weight comonomer(s) may be incorporated in PVDFcopolymer with from about 5% to 20% by weight being preferred. Resins ofterpolymers of VDF, particularly those of VDF, TFE and HFP may also beincorporated in the resins employed as starting materials.

Use of resins prepared by emulsion or suspension polymerization invertical or horizontal batch reactors or in continuous reactors iscontemplated by the invention.

The polymer resin may be obtained as a dried powder from the latexobtained during their synthesis suitable for blending into thecompositions of the invention by methods well known in the art whichneed not be detailed here. Such methods include: drying of latex,coagulation by high shear mixing, centrifugation, and/or altering theionic balance and/or freezing followed by filtration and optionalwashing and the like.

The polyamide 11 and polyamide 12 resin which are to be blended with thepolyvinylidene fluoride based resins are also well known articles ofcommerce and are both available in grades suitable for powder coatingapplication from Elf Atochem S.A. and its subsidiary company Elf AtochemNorth America, Inc.

Blending the PVDF resin and the polyamide resin may be accomplishedsimply by blending the powdered resins in the desired portions by weightusing any convenient standard powder blending technique.

If desired, pigment(s) (or other colorant(s)) may be incorporated at thetime of initial blending of the resins or it may be blended into thepreformed mixture at a later time. Pigment (or other colorant) may alsobe combined with either resins prior to blending of the resins and beintroduced into the mixtures in that fashion.

Any pigment (or other colorant) known to be useful in polyamide and/orpolyvinylidene fluoride based coatings may be employed.

The pigments may include, for example, those pigments identified in U.S.Pat. No. 3,340,222. The pigment (or other colorant) may be organic orinorganic. According to one embodiment, the pigment may comprisetitanium dioxide, or titanium dioxide in combination with one or moreother inorganic pigments wherein titanium dioxide comprises the majorpart of the combination. Inorganic pigments which may be used alone orin combination with titanium dioxide include, for example, silica, ironoxides of various colors, cadmium, lead titanate, and various silicates,for example, talc, diatomaceous earth, asbestos, mica, clay and basiclead silicate. Pigments which may be used in combination with titaniumdioxides include, for example, zinc oxide, zinc sulfide, zirconiumoxide, white lead, carbon black, lead chromate, leafing and non-leafingmetallic pigments, molybdate orange, calcium carbonate and bariumsulfate.

The preferred pigment category is the ceramic metal oxide type pigmentswhich are calcined.

Chromium oxides and some iron oxides of the calcined type may also besatisfactorily utilized. For applications where a white coating isdesired, a non-chalking, non-yellowing rutile-type of titanium dioxideis recommended. Lithopones and the like are inadequate as they sufferfrom lack of chalk resistance and/or from inadequate hiding. AnastaseTiO₂ is similarly not recommended.

The pigment (or other colorant) component, when present, isadvantageously present in the composition the amount of from about 0.1to about 50 parts by weight per 100 parts of resin component. While formost applications the preferred range is from about 5 to about 20 partsby weight pigment per 100 parts of resin component.

Clear metallic pigmented coats will have very low amounts by weight ofpigment.

The powder coating may be applied to the substrate by any knownconventional application method which will provide a uniform coating.Typical techniques are fluidized bed, thermal spray, or preferablyelectrostatic coating.

The powder coating may be applied to the substrate with or without aprimer coating. After application, the coating is subjected to atemperature above the melt temperature of the coating formulation,preferably between about 450° F. and 500° F. (232° to 260° C.).

Due to the high bake temperatures, the coatings are primarily useful ascoatings on metal substrates and similar thermally stable substrates,such as, aluminum, steel, glass and ceramics. The applications of suchcoated substrates are primarily decorative where long term UV resistanceand/or impact resistance are required. Typical examples are metalbuilding parts (window frames, door frames roofing, wall panels,furniture components and the like) and automotive components. Use asfunctional coatings (for corrosion and/or wear resistance, for example)is also contemplated.

Improved performance in such traditional uses of polyamide based powdercoatings such as dishwasher baskets, hot water heater tank liners,shopping carts, file rods and mechanical parts will be obtained.

Similarly, three-dimensional formed objects can be produced fromembodiments of the first composition aspect of the invention by lowshear methods conventionally employed for forming polyamide objects,such as injection molding, roto molding and the like, and the objects soformed will have superior use properties to objects formed by similarmethods from otherwise analogous polyamides not admixed with PVDFpolymers. For such uses, obviously, grades of polyamide known to besuitable for the forming technique will be selected by one of skill inthe art.

One of skill in the art will also recognize that the above describedapplication and fabrication methods are generally applicable in thepresence or absence of pigments or other colorants.

Examination of the surface of embodiments of the second compositionaspect of the invention by conventional analytical techniques such as,Scanning Electron Microscopy (SEM) and X-ray Photoelectron Spectroscopy(XPS) provides data consistent with a final structure having a greaterconcentration of PVDF based polymer on the surface. At PVDFconcentrations of about 5% by weight or greater, the data obtained isconsistent with a surface of substantially all PVDF based polymer withfew or no breaks in the PVDF based polymer layer.

The PVDF resin powder may be incorporated with the polyamide resinpowder in concentrations of from 0.01% up to 45% by weight depending onthe desired use properties of the final product. For normal powdercoating purposes from about 5% to about 15% by weight is preferred withabout 10% by weight being most preferred. For better surface decorativeappearance, concentrations of PVDF resin in the lower portion of theconcentration range are preferred. For increased stain and chemicalresistance, concentrations of PVDF resin in the higher ranges arepreferred.

One of skill in the art will also recognize that in addition to theafore described thermoplastic PVDF resins, other known thermoplasticfluoropolymers such as polytetrafluoroethylene and polyvinyl fluoridemay be employed in conjunction with or in place of the PVDF basedresins. The commonly known PVDF based fluoroelastomers and other knownfluoroelastomers are also contemplated as equivalents in the powderblends of the first composition aspect of the invention and in thecoated objects of the second composition aspect of the invention.

The following examples further illustrate the best mode contemplated bythe inventor for the practice of their invention and are intended to beillustrative and not in limitation thereof.

EXAMPLES 1 to 5

Blends of powder coating resin formulation were prepared from acommercially available PVDF based polymer in powder form (KYNAR® 711from Elf Atochem North America, Inc.) and commercially availablepigmented polyamide 11 resin powder (RILSAN® 5498HV FB from Elf AtochemNorth America, Inc.). The concentration value given for each examplerepresents the percent by weight PVDF based resin in the blend with thebalance being polyamide. The powder coating resin formulations werecoated on grit blasted steel or aluminum plates either unprimed orprimed with conventional epoxy phenolic primers known to enhance theadhesion of polyamides to metal substrates, using conventional fluidizedbed dipping techniques or electrostatic spray and then fused attemperatures above the fusion point of the resin powders. Propertiesdependent on the substrate, primer and application technique appearedrelatively constant among samples and consequently are not reported.

Surface characteristics reported are dependent on relative concentrationof the resins in the coating materials not on other factors for theseexamples.

Sample preparation: Representative samples were cut from each panel to asize of about 1 cm×1.5 cm. The samples were then coated withapproximately 50 nm of gold/palladium (60 sec. sputter) to reducesurface charging and specimen damage from electron irradiation in theSEM.

The high surface sensitivity of XPS demanded special surface preparationfor the XPS samples. The as-received surface of the samples aregenerally covered with a layer of particulate and organic contaminants(i.e. fingerprints, atmospheric dust, organic material). The layer ofcontaminants was removed by Carbon Dioxide Snow cleaning. This cleaningprocess carries away particulate and organic contaminants while leavingno harmful residue that would interfere with the surface analysis.

    ______________________________________                                        Example No. PVDF Resin Concentration                                          ______________________________________                                        1 (control) 0%                                                                  2 2%                                                                          3 5%                                                                          4&5 10%                                                                     ______________________________________                                    

Surface analysis by SEM:

Example 1

The surface was fairly smooth and featureless except for numerous cracksand white spots. The white spots are titanium based pigments.

Example 2

This surface showed a surface layer with circular "holes" through whicha polyamide type surface is visible. In conjunction with XPS resultsreported below, this is consistent with a layer of PVDF based polymer onthe surface, but one that is not continuous. The surface layer has threeregions: a structureless network type of region surrounding the exposedpolyamide areas, a smooth area with cracks resembling a dried outmudflat and circular growth regions with radial lines.

Example 3

The surface resembled the surface of Example 2 except no polyamideregions were visible. The surface contained some depressions and smallholes.

Examples 4 & 5

Very similar surface appearance to Example 3 but perhaps fewer holes.

Analysis by XPS:

In this technique, the sample is irradiated with monochromatic X-rayscausing electrons to be ejected by the Einstein photoelectric effect.These photoelectrons have characteristic energies unique to each elementin the periodic table. With sufficient energy resolution, the chemicalenvironment of the atoms may be inferred from small changes in thesecharacteristic energies. This method analyzes the topmost 10 nm of thesurface (electrons originating further down can not escape the surface)and is therefore very surface sensitive. The data consists of plots ofelectron counts versus energy in which each peak represents a specificelectron shell. Every element except hydrogen (which can sometimes beinferred from the chemical shifts) can be detected.

Surface analysis by XPS:

Low resolution survey spectra (0 to 1400 eV) were run for each surface.All significant peaks were identified by element. The surfaces containedmostly carbon, fluorine and oxygen. Trace amounts of nitrogen were alsofound, as expected, from the polyamide in the coating.

High resolution spectra were obtained for carbon, oxygen, fluorine andnitrogen. These high resolution spectra were used to quantify the amountof PVDF resin at the surface of the coating.

By comparing the subpeak positions for each element with standardtables, it is possible to estimate the amounts of polyamide and PVDFbased polymer present.

The results obtained are summarized:

Example 1--The data obtained matched those from polyamide extremelywell.

Example 2--Almost half the surface is polyamide.

This result is consistent with migration of PVDF resin to the surfacepreferentially.

Example 3--No detectable polyamide on the surface.

Examples 4 & 5--No detectable polyamide on the surface.

Examination for Gloss:

For all samples 60° Gloss was determined by ASTM D523-89.

Gloss was found to decrease over the value found for any particularpolyamide 11 sample applied by any particular technique to anyparticular substrate with increasing PVDF resin content.

Example 6

A roto molded tank was made from a blend, dry mixed in a Henschel mixer,of 90% by weight of a standard RILSAN® roto molding grade of polyamide11 (from Elf Atochem North America, Inc.) and 10% by weight KYNAR® 711,XPS analysis of the inner and outer surfaces as well as a cut surface.The results show a significant enrichment of the KYNAR fraction of theresin mixture on the inner surface. This result is consistent with theresults shown above for the powder coatings.

The subject matter which applicants regard as their invention isparticularly pointed out and distinctly claimed as follows:

We claim:
 1. A resin composition consisting essentially of:a) from 0.01%up to 45% by weight polyvinylidene fluoride based polymer; and b) fromgreater than 55% to 99.99% by weight polyamide polymer selected from thegroup consisting of polyamide 11 and polyamide
 12. 2. A resincomposition as defined in claim 1 wherein the polyamide is polyamide 11.